[FieldTrip] 4D-Neuroimaging Magnes 2500WH system

Ling Wang lingwang at m.scnu.edu.cn
Wed May 4 16:27:43 CEST 2016

Dear Sarang,

Thanks for your reply.

Our MEG system consists of 148 magnetometers. I searched the MEG papers published by researchers in your previous department at the University of Konstanz, and found two papers by Staudigl, Hanslmayr and colleagues (2013, 2015), in which the MEG data were collected with Magnes 2500WH 148-channel system and analyzed by FieldTrip. I'm happy about the papers. It seems that we can also use our MEG system to perform experiments. 

I'm new to the MEG field and am learning. Actually, I'm not sure about what the balancing weights are for. I read some scripts/functions of the FieldTrip toolbox, such as ft_read_header, bti2grad and read_4d_hdr. It says in the bti2grad function, "BTI2GRAD converts a 4D header to a gradiometer structure that can be understood by FieldTrip and Robert Oostenveld's low-level forward and inverse routines." So my understanding is that the balancing weights stored in hdr.grad is important for carrying out analyses at the source level? Or, the balancing weights are only necessary for gradieometers system but not for magnetometers system?

Thanks again for the information.

Best wishes,
------------------ Original ------------------
From:  "Sarang S. Dalal"<sarang at cfin.au.dk>;
Date:  Wed, May 4, 2016 06:50 PM
To:  "FieldTrip discussion list"<fieldtrip at science.ru.nl>; 

Subject:  Re: [FieldTrip] 4D-Neuroimaging Magnes 2500WH system

Dear Ling,

Does your system consist of 148 magnetometors or gradiometers? In my previous lab at the University of Konstanz, we also had the Magnes 2500WH with 148 magnetometers. In our experience, the weights were not necessary for analyses  at either the sensor or source level. If your system consists of gradiometers, however, maybe these weights would be necessary?

If you really need those weights, I believe you can find them in the header structure, somewhere in data.hdr.orig. You will then need some knowledge on how to apply those weights.





 From: fieldtrip-bounces at science.ru.nl <fieldtrip-bounces at science.ru.nl> on behalf of Ling Wang <lingwang at m.scnu.edu.cn>
 Sent: Wednesday, May 4, 2016 11:32 AM
 To: fieldtrip
 Subject: [FieldTrip] 4D-Neuroimaging Magnes 2500WH system  
  Dear All,
 We recently started a joint study with the staff of a hospital specialized for brain diseases, where there is a 4D-Neuroimaging Magnes 2500WH system. We have collected a sample MEG data with the system to see if we can perform experiments with the system. I am trying to analyze the data with FieldTrip. As introduced in the tutorial (http://www.fieldtriptoolbox.org/getting_started/bti), the software currently reads digital balancing weights only  for the Magnes 3600 system but not the 148-channel system. And yes, the software does not compute the balancing matrix for our MEG data, as indicated by the function, ft_read_header, "not applying digital weights in the  gradiometer balancing matrix", when reading our MEG data.
 I have three questions about analyzing these Magnes 2500WH MEG data with FieldTrip.
 1) Can we still carry out the analyses (ERF, TRF and connectivity) correctly at the sensory-level? 
 2) Is there a plan that FieldTrip would read the digital balancing weights for the MEG data of the Magnes 2500WH system?
 3) If we want to program to read the weights, what information do we need and possibly where can find the related information (e.g., the user manual of the system?)?
 Thanks in advance.
 Best wishes,
 Ling Wang
 School of Psychology
 South China Normal University
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